The availability of truck weight, dimension, classification and speed data is required for highway engineers in determining the structural and maintenance requirements of pavements and bridges. Accurate data of these types is also necessary for planning, economic and enforcement surveys.
Devices and methods for collecting these data are known to exist in both permanent and portable form. Most truck weight data is presently collected by static weigh stations operating at fixed locations on major highways. Fixed weigh stations, however, are costly and often ineffective due to scale avoidance and the limited amount of data collected at specific sites. Although a portable method of weighing a vehicle in motion is known, the method has not been widely implemented, due to the high cost of equipment and the need for well-trained operators of such equipment. Moreover, because operations are present at the weighing location, the operators are exposed to road hazards, and scale avoidance remains a problem.
A method of weighing a moving vehicle is suggested by Moses and Garson in "Probability Theory for Highway Bridge Fatigue Stresses", Report No. SMSMD No. 50 to Department of Transportation, Columbus, Ohio, July 1973. The report notes the correlation of peak strains sustained by bridge structures to gross vehicle weight of trucks passing over the structure. Measuring only the peak strains, however, does not provide sufficient information for estimating axle weights and gross weights of vehicles of all configurations.
Moses later disclosed a method for weighing a moving vehicle that used a least squares error minimization technique to calculate the individual vehicle axle weights, in "Weigh-in-Motion System Using Instrumented Bridges", Transportation Engineering Journal, ASCE, Vol. 105, May 1979. Inputs to the algorithm used in this technique are the entire strain record of the bridge structure as the vehicle crosses, and a function relating the position of each axle with time. This method of weighing a moving vehicle has had limited success, however, due to costly computing equipment and the functional limits imposed by using such equipment. In addition, the continued presence of operators at the weighing site is required.
Thus, there is a need for a portable, low-cost apparatus and method of weighing a vehicle in motion, using existing bridge structures, which can be operated unattended at an extended temperature range for extended periods of time. The present invention addresses this need.